BSC 314 Lecture Notes - Lecture 55: Archegonium, Zygote, Thallus
27 Jun 2018
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Phylum Sphenophyta: Horsetails
Only one herbaceous genus— Equisetum—of 15 species remains of this once large
group of woody trees of Carboniferous Age forests. Equisetum is one of the easiest
plants to recognize: It has jointed, ribbed and hollow stems impregnated with so much
silica that a rasping noise is heard when stems are rubbed together. Another of its
common names, “scouring rush”, indicates one of the early settlers' uses of the plants.
At each stem node there is a ring of small leaves fused in a sheath. Some species
additionally have a whorl of branches at each node, which gives rise to the “horsetail”
common name. The aerial shoots arise from an extensive rhizome
system. Equisetum sperm—like those of the rest of the ferns and fern allies—require an
external film of water in which to reach the eggs; Equisetum is most often found in sites
that are moist for at least part of the growing season. Sexual reproduction is not
necessary to propagate horsetails, however, which often spread vegetatively by means
of rhizomes.
Equisetum grows worldwide except for Australia, New Zealand, and
Antarctica. Most species grow in the Northern Hemisphere between about
40° and 60° N latitude. The modern plants resemble their arborescent
ancestors that grew 250 million years ago—which might make Equisetum the
oldest living vascular plant genus and the one least changed over time. The
horsetails have no commercial role and are of minor importance in natural
ecological systems.
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Document Summary
Only one herbaceous genus equisetum of 15 species remains of this once large group of woody trees of carboniferous age forests. Equisetum is one of the easiest plants to recognize: it has jointed, ribbed and hollow stems impregnated with so much silica that a rasping noise is heard when stems are rubbed together. Another of its common names, scouring rush , indicates one of the early settlers" uses of the plants. At each stem node there is a ring of small leaves fused in a sheath. Some species additionally have a whorl of branches at each node, which gives rise to the horsetail common name. The aerial shoots arise from an extensive rhizome system. Sexual reproduction is not necessary to propagate horsetails, however, which often spread vegetatively by means of rhizomes. Equisetum grows worldwide except for australia, new zealand, and. Most species grow in the northern hemisphere between about.
